Patent literature 1 discloses a brake system having (a) a hydraulic brake configured to restrain rotation of a wheel, (b) a master cylinder, (c) an accumulator, (d) a pressure increasing mechanism utilizing hydraulic pressure of the accumulator and activatable by activation of an electric actuator, (e) a selector valve configured to select a higher one of hydraulic pressure of the pressure increasing mechanism and hydraulic pressure of the master cylinder, and to supply the selected hydraulic pressure to a brake cylinder of the hydraulic brake, and (f) a pressure holding valve which is provided between the selector valve and the brake cylinder and which is a normally-open electromagnetic valve that is to be placed in an open state when electric current is not being supplied to a solenoid thereof.
Patent literature 2 discloses a brake system having (a) hydraulic brakes provided for front right, front left, rear right and rear left wheels of a vehicle and configured to restrain rotations of the wheels, (b) a master cylinder, (c) a mechanical booster mechanism provided between the master cylinder and brakes cylinders of ones of the hydraulic brakes which are provided for the front right and front left wheels, (d) a high pressure source and (e) linear control valves provided between the high pressure source and brake cylinders of the hydraulic brakes provided for the front right, front left, rear right and rear left wheels.
Patent literature 3 discloses a brake system having (a) a hydraulic brake activatable by hydraulic pressure of a brake cylinder and configured to restrain rotation of a wheel of a vehicle, (b) a master cylinder, (c) a master cut-off valve provided between the master cylinder and the brake cylinder, (d) a pressure holding valve that is a normally-open electromagnetic valve provided between the master cut-off valve and the brake cylinder, (e) a pressure reducing valve that is a normally-close electromagnetic valve provided between the brake cylinder and a low pressure source, and (f) a pump configured to pump a working fluid stored in a reservoir and to supply the working fluid onto an upstream side of the pressure holding valve. In this brake system, during execution of an anti-lock control, the hydraulic pressure of the brake cylinder is controlled by opening and closing the pressure holding valve and the pressure reducing valve in a state in which the brake cylinder is isolated from the master cylinder.